Writing Portable CGI

When developing CGI scripts, it is best to ensure configuration requirements are kept to a minimum. By using dynamic environment variables as opposed to absolute paths, you can make your scripts portable, thereby reducing script configuration requirements, even if the script is moved to a different system.

'DOCUMENT_ROOT'

Avoid absolute paths to supporting files (i.e. /usr/home/yourdomain.com/filename.txt). Use $ENV{'DOCUMENT_ROOT'}. By using the DOCUMENT_ROOT environment variable, your script will not be affected by changes to the server environment.

Description	Path
Home directory:	Absolute path: /usr/home/yourdomain.com Recommended path: $ENV{'DOCUMENT_ROOT'}/.. Standards-compliant approach: $homedir = $ENV{'DOCUMENT_ROOT'}; $homedir =~ s/\/htdocs$// || die;
Document root:	Absolute path: /usr/home/yourdomain.com/htdocs Recommended path: $ENV{'DOCUMENT_ROOT'}
"cgi-bin" directory:	Absolute path: /usr/home/yourdomain.com/htdocs/cgi-bin Recommended path: $ENV{'DOCUMENT_ROOT'}/cgi-bin

'SERVER_NAME'

Avoid absolute paths to the domain name. The domain name of the server is available via $ENV{'SERVER_NAME'}. By using the SERVER_NAME environment variable, you can avoid having to hard code the name of the server throughout the script. Your script will also be unaffected should the domain name change at a later date:

$myservername = $ENV{'HTTP_HOST'} || $ENV{'SERVER_NAME'};

'SCRIPT_NAME'

Aviod absolute paths to the script name. The name of the script is available via $ENV{'SCRIPT_NAME'}. By using the SCRIPT_NAME environment variable, you can avoid having to hard code the name of the script throughout your script. Your script will also be unaffected should you choose to rename it at a later date:

$myserver = $ENV{'HTTP_HOST'} || $ENV{'SERVER_NAME'};
$myurl = "http://$myserver$ENV{'SCRIPT_NAME'}";

'HTTPS'

Avoid hard coding "http://" or "https://" into the script. Use $ENV{'HTTPS'}. By using the HTTPS environment variable, your script will function correctly both on a normal web server, and on a secure server, and will not be affected should you choose to move it between these environments:

$myserver = $ENV{'HTTP_HOST'} || $ENV{'SERVER_NAME'};
$myhttp = $ENV{'HTTPS'} ? "https://" : "http://";
$myurl = "$myhttp$myserver$ENV{'SCRIPT_NAME'}";

Additional Environment Variables

There are many more environment variables that you can use. For details of all available variables, please visit http://www.yourdomain.com/cgi-bin/env.pl (replacing "yourdomain" with your actual domain name). This script was provided with your account.